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SubjectRe: [PATCH 2/2] coresight: tmc: Add shutdown callback for TMC ETR/ETF
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On 2020-06-03 13:26, Sai Prakash Ranjan wrote:
> Hi Robin,
>
> On 2020-06-03 17:51, Robin Murphy wrote:
>> On 2020-06-03 13:00, Sai Prakash Ranjan wrote:
>>> Hi Robin, Mathieu
>>>
>>> On 2020-06-03 17:07, Robin Murphy wrote:
>>>> On 2020-06-01 22:28, Mathieu Poirier wrote:
>>>>> That being said I'm sure that dependencies on an IOMMU isn't a
>>>>> problem confined
>>>>> to coresight. I am adding Robin Murphy, who added this commit [1],
>>>>> to the thread
>>>>> in the hope that he can provide guidance on the right way to do this.
>>>>
>>>> Right, it's not specific to CoreSight, and it's not even specific to
>>>> IOMMUs really. In short, blame kexec ;)
>>>>
>>>
>>> Yes it is not specific to coresight, we are targeting this for all
>>> consumers/clients of SMMU(atleast on SC7180 SoC). We have display
>>> throwing
>>> NoC/interconnect errors[1] during reboot after SMMU is disabled.
>>> This is also not specific to kexec either as you explained here [2]
>>> about
>>> a case with display which is exacly what is happening in our system [1].
>>
>> Sure, but those instances are begging the question of why the SMMU is
>> disabled at reboot in the first place ;)
>>
>
> That is what happens in SMMU shutdown callback right? It is the
> reboot/shutdown flow.

Yes, that's where it happens, but my point is *why* it happens at all.

hint: `git log --grep=shutdown drivers/iommu/`

If we could assume the system is always about to be powered off or
reset, we wouldn't need to do anything to the SMMU either ;)

Robin.

>
>    arm_smmu_device_shutdown()
>     platform_drv_shutdown()
>      device_shutdown()
>       kernel_restart_prepare()
>        kernel_restart()
>
> Thanks,
> Sai
>

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